Electronic systems are not completely closed systems. The current flowing through the circuits is not fully contained; rather it generates electromagnetic energy that can propagate around the circuit and tends to produce disturbance voltages in and around the system. Electronic circuits, therefore, have this tendency to radiate or pick up this undesired electromagnetic energy and it can seriously compromise the intended functionality of these circuits.
1. EMC – EMI
Electromagnetic Interference (or EMI) is the phenomenon that may occur when an electronics device is exposed to unwanted electromagnetic noise from an outside source. EMI can seriously affect the performance of devices. In case this interference lies in the Radio frequency spectrum, it’s called radio frequency interference or RFI.
Electromagnetic Compatibility (or EMC) is the ability of a device to function correctly in an environment with EMI, without affecting any other nearby equipment. The main goal of studying EMC is to ensure that all the side effects of EMI remain within a predefined safety limit.
2. Source of EMI:
The sources of EMI can be natural such as thunderstorm, lightening or solar radiation, or it can be man-made from other devices or systems such mobile phones, radars or motors etc. Most of the times, these disturbances are unintentional but can be intentional to create a hostile environment for enemy’s electronics devices, as is the case in Electronic Warfare (EW).
3. Effects of EMI:
Electromagnetic Interference can affect the performance of a system and may even damage it permanently. Depending upon the system under EMI stress, these effects may result in critical failures. It can cause circuits to blow up, trigger false activation signals for missile systems, cause errors in measuring systems, block communication systems and many others.
Effects of EMI (Source: ElectronicDesign.com)
One of the very common examples of EMI was the case when a mobile phone placed near a speaker can make the speaker generate ‘Bip-Bip’ noise. That happened because the mobile phone signals, although well above audio levels, modulated the signals at audio frequencies and were in turn amplified by the speaker.
Contrary to this relatively harmless example, the environment in military and space applications is really noisy and its impact can be seriously damaging in terms of catastrophic failures, loss of human lives and monetary losses.
A poorly designed device such as a mobile phone or even an oven can have severe impacts on human health. In the field of medical science, EMI can affect measuring devices and generate erroneous reports about a patient’s condition.
4. Significance of a Good EMC Design:
The above examples make the significance of a good EMC design really obvious. Today, we have more electronic devices in every domain of our lives than ever before. This also includes more and more wireless devices which mean a lot of electromagnetic signals in the environment around us. Advancements in Integrated Circuits technology is resulting in smaller and smaller devices reducing physical spacing between components in a device.
Effects of EMI (Source: BTH Group of Labs)
Consequently, the components in electronics devices are way too close with way too many electromagnetic signals around. Therefore, to ensure a reliable operation, the constraints on acceptable levels of EMI have grown really tight.
How well a system or device copes up with these constraints depends on how smartly it has been designed. This makes the job of an EMC engineer much more difficult yet significant.
Today, EMC is a major consideration in any project involving the design, manufacturing and installation of electrical and electronic equipment. It is imperative to ensure that the design not only meets functional requirements but it is also electromagnetically compatible with its operational environment.
EMC As Part of Design
By this point, we have established the importance of EMC considerations in design. It is, however, pertinent to mention that it is extremely important that these considerations be deemed as important as the original intended functionality of the system and they should be incorporated in the early stages of product development.
In other words, the product has to be designed as if it is intended to operate at a certain level of EMI environment. This becomes much more crucial in performance and safety critical systems such as military grade, avionics and space grade equipment.
Not incorporating EMC/EMI specifications at an early stage can result in the time and cost expensive redesign process which can, in turn, cause loss of market and consumer confidence and total product failure as well.
5. Basic Principles and Mechanism of EMC/EMI
EMC/EMI used to be characterized as a Black Magic but that is a story of the days long gone. Today we understand the principles governing EMC/EMI fully well. Therefore, having a sound understanding of these principles is, in fact, the first step towards a good EMC design.
EMC/EMI Basics (Source: Electronics-Notes.com)
- The circuit or device that generates unwanted electromagnetic energy is termed as Source, while the one that is exposed to this energy is referred to as Victim.
- The generation of unwanted electromagnetic energy is referred to as EM Emissions. These emissions must be kept below a certain acceptable limits to ensure no interference or disturbance to other equipment.
- The behavior of a device when it is exposed to EMI is known as its EM Susceptibility or Immunity. If a device performs well in EMI conditions, it is said to be less susceptible or more immune to EMI.
- There are two ways in which the EMI travels from the source to the victim; through the air as Radiations and/or conducted along or coupled onto I/O lines or power cables, termed as Conduction.
- Therefore, in order for a product to be EMC/EMI compliant, it has to be tested for its: a. Conducted Emissions b. Radiated Emissions c. Conducted Susceptibility d. Radiated Susceptibility
- There are some other relatively more unusual mechanisms of electromagnetic coupling which include capacitive coupling and induction.
- Another way to characterize EMI is with reference to its bandwidth. For instance, if the EMI is a single carrier source, such as from an oscillator, it is called Narrow Band EMI. Whereas, if the EMI is disturbing along multiple frequencies of the spectrum, it is said to be Wideband EMI.
6. EMC/EMI Standards
Just a few decades ago, the levels of EMC and EMI were low and the constraints were not too stringent. With the rather recent advancements in technology and growing awareness, it became inevitable to introduce EMC standards to meet the required level of electromagnetic compatibility and hence producing reliable and safer electronics systems.
However, different regions around the world, such as US or EU, have slightly varying standards. The other factor that decides which standard needs to be met by any certain product is the relevant industry. For instance, military standards, which are much tighter, will be applied to regard any product fit to be used in military applications.
7. Mitigation of EMI
The main job of an EMC engineer is to incorporate the EMC/EMI requirements of a product into its design so that the final product must meet the relevant EMC/EMI standard. However, in case any problem arises, it has to be approached from 3 different aspects which are as follows:
- The internal source of Emissions has to be eliminated.
- The external source of Interference has to be suppressed.
- The overall design has to be made EM immune or EM hardened.
EMC/EMI Testing (Source: 3ctest.co.uk)
The best approach to tackle this problem is to start taking care of emissions, since these are the main source of EMI.
- Radiated emissions can be taken care of by Shielding that is the use of metallic housing of the equipment and shielded cables.
- After that, conducted emissions through cabling and I/O lines can be controlled by appropriate
- Finally, proper Grounding/Earthing ensures that the EM energy will travel to the ground level and hence out of the system.
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1. “Design for EMC” presentation by Daryl Gerke, PE
10. Jeffrey O. Grady, in System Requirements Analysis (Second Edition), 2014